System, method and apparatus for regulating the light emitted by a light source

ABSTRACT

In one embodiment, apparatus is provided with a light source, an optic element, at least one photosensor, and a control system. The optic element has a reflective material on a surface thereof, and is positioned to receive and reflect light emitted by the light source. The at least one photosensor is mounted to the surface of the optic element on which the reflective material resides, over a portion of the optic element on which the reflective material does not reside. The control system is operably associated with both the photosensor(s) and the light source, to regulate the light source&#39;s light output in accordance with measurements received from the photosensor(s).

BACKGROUND

A problem with light sources comprised of one or more solid-state lightemitters (e.g., light emitting diodes) is that the intensity of lightemitted by a solid-state light emitter is subject to change as a resultof changes in its temperature and aging. Furthermore, thecharacteristics (and thus the light emitting capabilities) ofsolid-state light emitters may vary from batch to batch. As a result, insystems where the integrity of light emitted by a light source needs tobe maintained (e.g., in display backlighting and illumination systems),some sort of system is needed to measure and regulate the light source'slight.

SUMMARY OF THE INVENTION

In one embodiment, apparatus comprises a light source, an optic element,at least one photosensor, and a control system. The optic element has areflective material on a surface thereof, and is positioned to receiveand reflect light emitted by the light source. The at least onephotosensor is mounted to the surface of the optic element on which thereflective material resides, over a portion of the optic element onwhich the reflective material does not reside. The control system isoperably associated with both the photosensor(s) and the light source,to regulate the light source's light output in accordance withmeasurements received from the photosensor(s).

In another embodiment, a method comprises projecting a light through anoptic element having a reflective material on a surface thereof. Thelight is then measured using at least one photosensor that is mountedover one or more non-reflective apertures in the reflective material onthe optic element. Thereafter, the light is regulated in accordance withmeasurements taken by the photosensor(s).

In yet another embodiment, a display system comprises a light source. Aprism has a reflective material on a surface thereof, and is positionedto receive and reflect light emitted by the light source. At least onephotosensor is mounted to the surface of the optic element on which thereflective material resides, over a portion of the optic element onwhich the reflective material does not reside. A display is positionedto be illuminated by light exiting the optic element. A first opticassembly having a lens is positioned between the light source and theprism; and a second optic assembly having a lens is positioned betweenthe prism and the display. A control system is operably associated withboth the photosensor(s) and the light source, and regulates the lightsource's light output in accordance with measurements received from thephotosensor(s).

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative and presently preferred embodiments of the invention areillustrated in the drawings, in which:

FIG. 1 illustrates an exemplary method for regulating the light emittedby a light source;

FIG. 2 illustrates a block diagram of an exemplary system for regulatingthe light emitted by a light source;

FIG. 3 illustrates an exemplary single photosensor embodiment of theFIG. 2 system;

FIG. 4 illustrates an exemplary multi-photosensor embodiment of the FIG.2 system; and

FIG. 5 illustrates an exemplary display system comprising three of thesystems shown in FIG. 4.

DETAILED DESCRIPTION OF AN EMBODIMENT

Micro-displays, such as liquid crystal on silicon (LCOS) displays,liquid crystal displays (LCDs), and digital micro mirror devices (DMDs),often use filament-based, discharge, white-light lamps to illuminatetheir displays. Depending on the technology, the displays may be lightedin a transmissive or reflective manner. While filament-based lampsprovide good color and consistent brightness (intensity), they generatea lot of heat, have relatively short lifespans, and are not shockresistant. To reduce the cost and increase the efficiency ofmicro-displays, it would be desirable to replace their filament-basedlamps with solid-state light sources, such as light emitting diode (LED)light sources.

LEDs pose to be a useful light source in that they are inexpensive tomanufacture, are widely available, and do not generate a lot of heat.However, the physical and electrical characteristics of LEDs (e.g.,turn-on voltage) can vary from batch to batch, leading to nominallyidentical LEDs having different optical properties. Furthermore, theoptical properties of LEDs can change or deteriorate with factors suchas changes in temperature and age. As a result, in systems where theintegrity of light emitted by a light source needs to be maintained(e.g., in a display backlight or illumination system where the intensityand/or color of a light source needs to be maintained), some sort ofsystem is needed to measure and regulate the light source's light.

FIG. 1 illustrates an exemplary method 100 for regulating the light (λ,FIG. 2) emitted by a light source 202. In accordance with the method100, light is projected 102 through an optic element 204 having areflective material 206 on a surface thereof (see also, FIG. 2). By wayof example, the optic element 204 can be a mirror, flexible film orprism. Also, and by way of example, the reflective material can be areflective coating on the optic element 204 (e.g., a silver coating), ora thin, reflective film (e.g., a foil).

The method 100 continues with a measurement 104 of the light using atleast one photosensor 208. The photosensor(s) 208 is/are mounted to thesurface of the optic element 204 on which the reflective material 206resides, over a portion of the optic element 204 on which the reflectivematerial 206 does not reside. By way of example, the photosensor(s) 208may comprise one or more photodiodes or phototransistors that measurethe intensity of one or more wavelengths of light.

After measuring the light, the light can then be regulated 106 inaccordance with the measurements taken by the photosensor(s). In oneembodiment, this is done via the feedback system 210, 212 shown in FIG.2.

By way of example, a light may be regulated by comparing at least oneintensity measurement received from the photosensor(s) (208) with atleast one desired intensity. Then, if an intensity measurement is out ofrange, the light source 202 may be adjusted.

As partially introduced, FIG. 2 illustrates an exemplary illuminationsystem 200 comprising a light source 202, an optic element (prism) 204having a reflective coating 206 thereon, and a photosensor 208. Theoptic element is positioned in front of the light source 202 to receiveand reflect light (λ) that is emitted by the light source 202. Inaddition to reflecting the light, the prism 204 may also mix and/orfilter the light. Preferably, the photosensor(s) 208 are positionedadjacent one another, and are positioned over one or more non-reflectiveapertures in the reflective coating 206 on the optic element 204.

Mounting the photosensor 208 on the optic element 204 can beadvantageous because it does not block the light (λ), thereby causingsubstantial light loss or otherwise interfering with light mixing.Rather, the position of the photosensor 208 requires only a smallnon-reflective aperture in the reflective material 206, and thus only asmall amount of light need be allowed to leak out of the reflective sideof the optic element 204.

The system 200 also comprises a control system 212. The control system212 is operably associated with both the photosensor(s) 208 and thelight source 202, and thereby regulates the light source's light outputin accordance with measurements (e.g., light intensity measurements)received from the photosensor(s) 208.

FIG. 3 illustrates an exemplary single photosensor embodiment 300 of thesystem 200, while FIG. 4 illustrates an exemplary multi-photosensorembodiment of the system 200. In the system 400, different lightintensity readings are obtained from a plurality of photosensors 402,404, 406 that are filtered in different ways so as to measure differentwavelengths of light (e.g., red, green and blue light).

In each of the systems 300, 400, the light source 202 may comprisesolid-state light emitting elements such as LEDs or laser diodes. By wayof example, the systems 300, 400 are shown to comprise red (R), green(G) and blue (B) LEDs. Although one of each is shown, the light source202 could alternately comprise any number or arrangement of the same ordifferent colored LEDs. In some cases, the light source 202 could alsobe limited to only a single light emitting element. If this is the case,it might only be possible to control the intensity, and not the color,of the light source 202.

The exemplary embodiment of the control system 212 shown in FIGS. 3 & 4comprises driver circuitry 302, a color management system 304, and amicrocontroller 306. The boundaries between components 302-306 aresomewhat arbitrary, and the functionality of the different components302-306 could alternately be merged or further divided. In use, thecolor management system 304 receives color and/or intensity settingsfrom the microcontroller 306, and converts the color setting (ifprovided) to a plurality of intensity settings for the different coloredlight emitting elements of the light source 202. The color managementsystem 304 also receives intensity measurements from the photosensor 208(FIG. 3) or photosensors 402-406 (FIG. 4). The color management system304 then compares corresponding intensity measurements, and if ameasurement is out of range, it adjusts the light output of acorresponding light emitting element by, for example, modulating itsdrive current.

By raising or lowering the drive currents of all light emitting elementsin unison, the color management system 304 can thereby control theintensity of the light source 202. By adjusting the ratios of drivecurrents supplied to the light emitting elements, the color managementsystem 304 can control the color of the light source.

The systems 300, 400 shown in FIGS. 3 & 4 may further compriseadditional components, including first and second optics assemblies 308,310. As shown, the first optics assembly 308 may comprise both apiano-convex 312 and a plano-concave 314 lens, arranged in seriesbetween the light source 202 and the prism 204 to first focus the lightproduced by the light source 202, and then collimate the light prior toit being received by the prism 204. The second optics assembly 310 maycomprise a plano-convex lens 310 to further focus the light onto adisplay 316, or a device or subject being illuminated. The display 316may take a variety of forms, including that of a micro-display.

In some cases, one or more of the systems 300, 400 may be used to lighta display 316 in the same manner. For example, one or more systems 300,400 could each project a white light onto a display 316. In other cases,and as shown in FIG. 5, a plurality of systems 400 a, 400 b, 400 c mayeach be tuned to project a particular color of light (e.g., red (R),green (G) and blue (B)) on a display 502. Although FIG. 5 shows eachdifferent color to be projected on a different portion of the display502, each color could alternately be scattered to illuminate the wholeof display 502.

1. Apparatus, comprising: a light source; an optic element having areflective material on a surface thereof, the optic element beingpositioned to receive and reflect light emitted by the light source; atleast one photosensor, mounted to the surface of the optic element onwhich the reflective material resides, over a portion of the opticelement on which the reflective material does not reside; and a controlsystem, operably associated with both the photosensor(s) and the lightsource, to regulate the light source's light output in accordance withmeasurements received from the photosensor(s).
 2. The apparatus of claim1, wherein the optic element is a prism.
 3. The apparatus of claim 1,wherein the optic element is a mirror.
 4. The apparatus of claim 1,wherein the optic element is a flexible film.
 5. The apparatus of claim1, wherein the reflective material is a coating on the optic element. 6.The apparatus of claim 5, wherein the coating comprises silver.
 7. Theapparatus of claim 1, further comprising a display, positioned to beilluminated by light exiting the optic element.
 8. The apparatus ofclaim 7, further comprising: a first optics assembly having a lens,positioned between the light source and the optic element; and a secondoptics assembly having a lens, positioned between the optic element andthe display.
 9. The apparatus of claim 1, wherein at least two differentphotosensors have differently filtered inputs and measure differentwavelengths of light.
 10. The apparatus of claim 1, wherein the lightsource comprises red, green and blue light emitting elements; whereindifferent photosensors measure red, green and blue wavelengths of light;and wherein the control system separately regulates the intensities ofthe red, green and blue light emitting elements in accordance with themeasurements received from the photosensors.
 11. The apparatus of claim10, wherein the light emitting elements comprise light emitting diodes(LEDs).
 12. The apparatus of claim 1, wherein the light source comprisesat least one solid-state light emitting element.
 13. The apparatus ofclaim 1, wherein the light source comprises one or more light emittingdiodes (LEDs).
 14. The apparatus of claim 1, wherein the photosensorsare positioned adjacent one another.
 15. The apparatus of claim 1,wherein the photosensors are mounted over one or more non-reflectiveapertures in the reflective material.
 16. A method, comprising:projecting a light through an optic element having a reflective materialon a surface thereof; measuring the light using at least one photosensormounted to the surface of the optic element on which the reflectivematerial resides, over a portion of the optic element on which thereflective material does not reside; and regulating the light inaccordance with measurements taken by the photosensor(s).
 17. The methodof claim 16, wherein different ones of the photosensors measure red,green and blue wavelengths of light; and wherein the light is regulatedby separately regulating red, green and blue light emitting elementsthat generate the light.
 18. The method of claim 16, wherein the lightis regulated by: comparing i) at least one intensity measurementreceived from the at least one photosensor with ii) at least one desiredintensity; and if an intensity measurement is out of range, adjustingthe light.
 19. The method of claim 16, wherein the optic element is aprism.
 20. A display system, comprising: a light source; a prism havinga reflective material on a surface thereof, the prism being positionedto receive and reflect light emitted by the light source; at least onephotosensor, mounted to the surface of the optic element on which thereflective material resides, over a portion of the optic element onwhich the reflective material does not reside; a display, positioned tobe illuminated by light exiting the optic element; a first opticsassembly having a lens, positioned between the light source and theprism; a second optics assembly having a lens, positioned between theprism and the display; and a control system, operably associated withboth the photosensor(s) and the light source, to regulate the lightsource's light output in accordance with measurements received from thephotosensor(s).